Powered exoskeleton rehabilitation devices have been proposed to assist the user's locomotion providing supportive force on the knee joint such as weight bearing. However, most of the current devices suffer from bulky and heavy design, a lack of active interaction between user and device, intuitive adjustment to the environment and pre-programmed walking trajectory.
Gait abnormality in the knee joint are very common among elders and post-stroke patients. Stroke is one of the primary causes of long-term disabilities, which affect their independency and the walking ability. Stroke may result in knee instability coupled with hyperextension. It is characterized by an extension of the knee joint beyond the neutral position, which could either occur rapid and abrupt or slowly during the gait cycle. Patients with a hyperextension acquire an abnormal gait pattern, which can increase the energy expenditure, reduce the ability to balance and can lead to pain, capsular and ligamentous laxity and/or bone deformity.
Another effect is the resulting adduction moment during the gait adaption, which increase the lateral distraction forces on the medial tibiofemoral unit. This can lead to pain in the medial tibiofemoral and/or posterolateral soft tissues and/or can lead to abnormal tibiofemoral alignments such as varus malalignment or anterior-posterior tibial slope. Other secondary medical problems of genu recurvatum are: joint contractures, osteoporosis, and pressure ulcer.
The normal gait pattern requires an adequate push-off by the gastrocnemius and soleus, a sufficient contraction of the quadriceps during the midstance, flexion of the hip and knee joint during the swing phase, and good balance and posture. Therefore, an effective gait recovery should incorporate those specific requirements in order to avoid an abnormal gait pattern or a hyperextension gait mechanism.
Gait recovery could be achieved by several rehabilitation means. In orthotics approach, stroke patients could be prescribed with lightweight knee-ankle-foot orthosis (KAFO) that can stabilize the knee and ankle joint. However, the training effect of the KAFO is limited. Physiotherapy (PT) and occupational therapy (OT) on the other hand are common interventions to enhance motor functions and slow down the progression of impaired mobility. Traditional therapy techniques include gait training, such as; over-ground, treadmill, motor relearning program, proprioceptive neuromuscular facilitation techniques, and Bobath-method. Previous studies showed that although these rehabilitation programs could reduce the severity of neuromuscular impairments, the effects were not task-specific, were limited to the targeted area only, and patients tend to adapt to compensatory strategies instead.
Lower limb exoskeleton robotic devices on the other hand, have become increasingly popular over the past few years. These robotic devices are designed to provide both walking assistance and body weight support, which is the combination of the PT, OT, and orthotics approaches. Previous studies reported positive therapeutic effects of robot-assisted gait training of stroke patients, for instance; improvements in walking independence, functional walking ability, muscle activation, walking speed, muscle tone, and range of motion.
Although research has shown that the use of robotic training systems can enhance the mobility of the patients and facilitate the rehabilitation progress most of the existing devices are mainly designed to move both legs, limited to treadmill use, lack of active human-robot interaction, limited to pre-programmed walking trajectory, missing intuitive adjustment to the walking environment, and voluntary residual motor intention is seldom involved in these systems.
However, stroke patients and persons with knee problems are only affected on one leg, which has still residual motor functions, while the unaffected leg supports the body weight and help to maintain balance. The main problem of persons who sustained a stroke is the lack of knee control during the gait cycle, due to the muscle weakness in the quadriceps and hamstring muscles and the hyperextension in the knee joint. The exoskeleton robotic knee system is designed to be lightweight, has the ability to be applied on unilateral side and fully adapt the movement of the device to the patient's activity (stairs climbing, sit-to-stand).